1. Field of the Invention
This invention relates to the positioning of hip sockets into prepared cavities int eh acetabulum of the pelvis in total hip joint replacement. The invention also relates to apparatus for this purpose, to the design and construction of such apparatus, as well as to a method of using the apparatus, and applies to all types of sockets, adhesives, and inserters which may be employed in the method. The invention also relates to apparatus for training surgeons int he placement of acetabular implants in hip joint replacements.
2. Description of the Prior Art
In hip joint replacement, it is common practice to utilise a socket inserting instrument, for example, typically a Charnley socket holder and orientation guide, for holding and introducing a polyethylene socket into the prepared cavity in the acetabulum of the pelvis. This socket holder is constructed to hold the socket on a free end extremity of a rod. A handle is fixed to the rod in the vicinity of its other end. The handle may typically be at right-angles to the longitudinal axis o the rod but other angles may also be used. A suitable adhesive is introduced into the prepared acetabular cavity and on the mating face of the socket, and the socket is then inserted into the cavity, using the socket holder. The surgeon holds the socket holder and manoeuvres it manually to orientate the socket into a disposition which is established by the skill, judgement and experience of the surgeon. In essence, the surgeon uses a visual method in which he tries to align two perpendicular straight bars defining the rod of the Charnley device and its handle, one of the bars being aligned with the longitudinal axis of the body and the other bar being aligned wit the transverse axis through the pelvis. However, since during a hip joint replacement operation, the patient's body is in a twisted position and is also covered with sterile cloths, the carrying out of this known method is not only extremely difficult but is also somewhat haphazard.
As a result therefore, a significant proportion of sockets cemented into cavities in hip joint replacement operations are disposed at an incorrect angle and this may cause the replacement hip joint to become dislocated. Dislocation may occur in particular if the legs are moved excessively far apart, in which circumstances the joint may actually come apart. Such a result causes great problems, not to mention actual pain, for the patient involved. A particular difficulty experienced by a surgeon in optimising the orientation of the socket arises form the absence of any straightforward method of defining a reference plane on the pelvis relative to which the appropriate angle may be set out. In addition the instruments currently available are not equipped with scales or protractors to supplement the visual judgement of the surgeon and his manual dexterity.